arm: fix array-out-of-bounds upon register parsing error

Despite the comment ahead of the enum explicitly pointing out the need
to also update the corresponding array, 1b8833198c0 ("Add support for
MVE instructions: vcmp and vpt") failed to do so. Oddly enough the issue
appears to be spotted only by rather old gcc (4.3-ish in my case).
diff --git a/gas/ChangeLog b/gas/ChangeLog
index 7133c37..ab12ba5 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,5 +1,9 @@
 2021-06-10  Jan Beulich  <jbeulich@suse.com>
 
+	* config/tc-arm.c (reg_expected_msgs): Add REG_TYPE_ZR entry.
+
+2021-06-10  Jan Beulich  <jbeulich@suse.com>
+
 	* config/tc-i386.c (optimize_encoding): Suppress LEA conversion
 	when it would grow code size in 16-bit mode.
 	* testsuite/gas/i386/lea16-optimize.d: Adjust expectations.
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 1e2ac65..895718c 100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -729,7 +729,8 @@
   [REG_TYPE_MMXWCG] = N_("iWMMXt scalar register expected"),
   [REG_TYPE_XSCALE] = N_("XScale accumulator register expected"),
   [REG_TYPE_MQ]	    = N_("MVE vector register expected"),
-  [REG_TYPE_RNB]    = ""
+  [REG_TYPE_RNB]    = "",
+  [REG_TYPE_ZR]     = N_("ZR register expected"),
 };
 
 /* Some well known registers that we refer to directly elsewhere.  */